Document cameras and other digital cameras increasingly have higher resolution digital imaging sensors, ranging from 2 MPixel, 5 MPixel, 10 MPixel, to 30 MPixel and even 40 MPixel, and will have even higher resolutions in the future. When a live preview of the video feed from these cameras is desired to be shown on a display or a host computer, several factors significantly limit the video display speed, (often referred to as the “smoothness” of the video) measured in frames per second (fps) of the host computer.
With reference to FIG. 1, a document camera 2 or other digital camera has been composed of a system of embedded electronics which include CMOS or CCD Sensors working in conjunction with Digital Signal Processing (DSP) processors, field programmable gate arrays (FPGA) processors, or ARM processors. Cameras based on these processors are capable of sending out high definition (HD) video at very high frame rates, such as 1080P HD video at sixty frames per second. However, 1080P, which is today's highest display resolution on consumer oriented HD TV's, is only roughly 2 MPixel in resolution, while sensor resolution is going far beyond to 10×or even 20× the 1080P resolution, and ever increasing. So video displays on HDTV screens can often deliver 60 fps but are unable to take full advantage of the camera sensor's high resolution.
Live video feed from a digital camera transmitted to a host computer, normally requires a USB 2.0 or USB 3.0 connector, and can deliver full frame images with the maximum sensor resolution; however, the live video feed often suffers from the limited bandwidth of USB channels, which results in very low video frame rates.
A host computer's display screen is most likely to have less resolution than the imaging sensor. In the past, a digital camera sent images directly to a host computer at whatever resolution the digital camera received the images from the digital camera's sensor outputs. The previous method jams up the data link easily, and causes low frame rates when displaying video images on the host computer's monitor.
Scalar software is currently present on digital camera devices. Images are scaled to a set of predefined resolutions on the camera device. Image output is one directional to the host computer or other display terminals. The “predefined” resolution sets severely limit the dexterity of these systems. Moreover, the predefined resolutions may not maximize the resolution of the display due to mismatched resolution values of the predefined resolution versus the display resolution of the host computer's display terminal.
Further, large sized video frame data must be transferred across limited bandwidth connections between the digital imaging device and the host computer. When frame resolution is high, this results in unacceptably low frame rate transfer for visual display on the host computer. To overcome such USB bandwidth limitations, image compression using Motion JPEG or H.264 encoding techniques is often employed. However, image compression often results in loss of image clarity due to the nature of most compression algorithms. Encoding of video on the camera and decoding on the host computer can also require significant processing overhead, which increases cost and causes low frame rates while displaying.